The present invention relates to ultrasonic medical imaging devices and, in particular, to a method of automatic elasticity image formation in which each elasticity image is accompanied by a quality measure that can be used for the purpose of operator feedback or automatic image selection.
Elasticity (E-mode) imaging reveals the stiffness properties of tissue, for example, strain, Poisson's ratio, and Young's modulus. The stiffness measurements may be collected over an area or volume and then mapped to a gray or color scale to form a two- or three-dimensional E-mode image.
In quasi-static elasticity imaging, images of the tissue in different states of deformation are obtained by ultrasonic or other imaging devices. Strain is deduced from two images by computing a gradient in displacement between the images along any desired direction. Quasi-static elasticity imaging is analogous to a physician's palpation of the tissue during which the physician determines stiffness by pressing the tissue and detecting the amount of tissue yield under this pressure.
The tissue deformation may be obtained manually, for example, by moving the ultrasonic transducer toward and away from the tissue or through a separate compressor mechanism or by physiological movement. Manual deformation of the tissue provides an extremely versatile technique that can be used with standard ultrasonic imaging equipment; however, manual deformation requires considerable operator skill. Ideally, for example, the deformation is at an angle and in an amount to reduce lateral tissue slippage while obtaining appropriate tissue displacement. Too much or too little deformation will not yield consistent E-mode image data.
Often E-mode image data is presented as a time series animation so as to provide an additional dimension of information to the physician. Low quality images incorporated into this animation can create disruptive breaks in the animation obscuring the extra dimension of information hoped to be obtained. Multiple E-mode images may be combined to reduce image noise or provide E-mode measurements along different axes. Again, low quality images incorporated into this combination decrease the quality of the measurement.